RP EXP31130A was applied on two application dates on mowed, irrigated turf-type perennial ryegrass during the late summer of 1995. There was no significant effects (responses) to the compound on perennial ryegrass. Only a slight (non-significant) color change occurred, which was not evident to the observer. No visual changes in turfgrass density, discoloration or stunting occurred, regardless of rates or sequential applications. Based on rates and timings conducted from these tests it appears initially that RP EXP31130A is very safe on perennial ryegrass turf mowed at 2.75 inches, when applied during the summer.

The experimental compound, RP-EXP31130A was tested for turfgrass tolerance under irrigated conditions in the Southwest. Rates and timing applications were evaluated for this new herbicide to assess the potential effects on perennial ryegrass. Turf tolerance is an important function as well as efficacy, and tolerance influences the type of turf a herbicide(s) can be safely used on, or if effects are realized, to what extent do they occur and for what length of time. This information is necessary for developing use rates, timing, and product applications in the turfgrass industry.

The material applied to the turf was the 75 WG formulation of RP-EXP31130A. The turf was irrigated with secondary effluent to prevent moisture stress. The turf was mowed two times weekly at 2.75 inches. Based on the above objectives, the RP-EXP31130A herbicide treatments were as applied at the following AI/A rates.

INITIAL APPLICATION SEQUENTIAL APPLICATION

0.18 lb + 0. lb

0.18 lb + 0.18 lb

0.18 lb + 0.36 lb

0.36 lb + 0. lb

0.36 lb + 0.18 lb

0.36 lb + 0.36 lb

All tests included a control. Each treatment appeared four times in a completely randomized block design. Initial and sequential applications were made on August 1 and September 4, 1995, respectively. Materials were applied using a Co₂ compressed air sprayer, using 8004 size nozzles on a three nozzle boom hand held sprayer (20 inch spacing). A total volume of 51 gallons per acre was applied between 500-600 a.m. and watered in within 3 hours after applications via standard turf overhead sprinklers.

The turf was observed for any signs of discoloration, turfgrass damage, or notable changes in density, etc. For this turfgrass species, response observations of turfgrass color was noted throughout the course of development. Observations are noted on days after treatment for each application (response/DAT/N), where N = (1) initial or (2) sequential application. Observation dates were based on expression development, which may have varied in type and number based on the particular turf in question.

Color scores were assigned on five dates (DAT/1) after the first application made on 8/1/95, and again on three dates (DAT/2) after the sequential treatments were applied on 9/4/95. On no dates were there significant treatment effects due to the application of EXP31130A on "Palmer" perennial ryegrass. Only the slightest difference in color change resulted, which would otherwise go undetected in a commercial situation. On August 4 (3 DAT/1), mean color scores ranged from 6.3 to 7.0, with the check having the highest value. Once again, the effect was non-significant. At 3, 8, 11, and 18 DAT/1, the check ranged as either the highest or second highest for mean turfgrass color, but was not so at 28 DAT/1. This is often a typical latent turfgrass response at about 30 DAT from herbicide or PGR applications.

Following the sequential application on 9/4/95, again there was no treatment effect, nor were there rate order trends. At no time did bleaching (loss of chlorophyll) occur, nor were there any visible signs of decreased turf density, discoloration, or tip burning. All applications were summer applied.

FN:RPRYE.95 DIR:Q495

Table 1. Mean color¹ response of turf type perennial ryegrass to applications of RP EXP31130A herbicide. University of Arizona, Summer 1995.

Check 7.0 7.0 6.5 7.8 6.8 6.8 6.8 7.0

.18+0 6.8 6.8 6.5 7.3 7.3 6.8 6.0 7.5

.18+.18 6.8 6.8 6.8 7.8 7.0 6.0 6.3 6.0

.18+.36 6.3 6.8 7.0 7.0 6.8 6.8 5.8 6.5

.36+0 6.8 6.5 6.8 7.0 6.8 6.5 6.3 6.8

.36+.18 6.8 6.8 6.5 7.3 6.7 6.5 5.8 6.8

.36+.36 6.8 6.8 6.8 7.0 7.3 6.5 6.0 6.8

LSD Value⁵ -- -- -- -- -- -- -- --

²Rate of lbs. product AI/A.

³Number of days after treatment on each test date.

⁴Mean of all treatments on each date.

⁵LSD Value = least significant difference value. Means with difference greater than LSD statistics are significantly different from each other.